/**
 * Copyright (C) 2009 Matteo Merli <mm@merlimat.org>
 * 
 * $Id: None.java 21 2009-01-12 17:30:19Z matteo.merli $
 * $URL: http://pxl-lang.googlecode.com/svn/trunk/src/main/java/pxl/types/None.java $
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *         http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package pxl.types;

import java.util.Collection;

import pxl.errors.TypeError;
import pxl.types.annotations.Exported;

/**
 * @author Matteo Merli
 */
public final class None extends PxlObject
{

    private static final PxlString NoneString = new PxlString( "None" );

    private static final None instance = new None();

    private None()
    {
    }

    public static None instance()
    {
        return instance;
    }

    @Override
    public String toString()
    {
        return "None";
    }

    @Override
    public String getType()
    {
        return "None";
    }

    // Operators

    @Exported
    @Override
    public PxlBoolean __eq__( PxlObject other )
    {
        return PxlBoolean.valueOf( other instanceof None );
    }

    @Exported
    @Override
    public PxlBoolean __neq__( PxlObject other )
    {
        return PxlBoolean.not( __eq__( other ) );
    }

    @Override
    public PxlString __str__()
    {
        return NoneString;
    }

    @Override
    public PxlString __repr__()
    {
        return NoneString;
    }

    @Override
    public PxlBoolean __bool__()
    {
        return PxlBoolean.False;
    }

    @Override
    public void __setattr__( String attrName, PxlObject value )
    {
        throw new TypeError( "Cannot set an attribute on the None object." );
    }

    // Attributes

    @Override
    protected PxlObject getAttribute( String name )
    {
        return null;
    }

    @Override
    protected Collection<String> getAttributeNames()
    {
        return null;
    }
}
